Greenwire [Printer-friendly version]
October 4, 2007
WATER WOES LOOM AS THIRSTY GENERATORS FACE CLIMATE CHANGE
By Katherine Ling, Greenwire reporter
U.S. power generators girding for possible mandatory curbs on
greenhouse gas emissions may also find themselves facing another
climate-related crisis: water shortages.
This past summer -- unusually hot and dry in many regions -- offered a
preview.
As electricity demand surged to keep air conditioners whirring, power
plants confronted shortages of cooling water that forced shutdowns and
led to inefficient operations. And that problem is expected to worsen
as climate change intensifies summer heat waves and droughts in
already-arid areas.
Water is no longer an afterthought for power plant planners, said Bob
Goldstein, the Electric Power Research Institute's senior technical
executive for water and ecological systems. That wasn't the case so
long ago when proximity to transmission lines and fuel dominated power
companies' planning.
"After you chose what type of plant you were going to build and site
it, then you went about getting the water," Goldstein said. "Now, you
have to consider the water up front as you decide where you are going
to build it."
Electric generators are facing growing competition for water from
thirsty cities, sprawling farms and new environmental regulations
aimed at protecting aquatic resources and recreational activities.
"Power plants are the last group in the queue," said Tom Feeley,
technology manager for the National Energy Technology Laboratory's
(NETL) Innovations for Existing Plants Program.
If current trends continue, power plants will be withdrawing 7.3
billion gallons a day by 2030 -- equal to all U.S. water consumption a
decade ago, according to a Department of Energy report.
Ironically, nuclear power plants -- touted by the nuclear industry and
its supporters as the answer to global climate woes because reactors
don't emit greenhouse gases -- need more freshwater to keep from
overheating than other generators.
Thirsty reactors
The average reactor needs more than 830 gallons of freshwater per
megawatt hour. All but about 3 percent of that is returned to the
stream, but it returns much warmer, the Energy Department said in a
report to Congress last year.
Nuclear plants' thirst proved a problem this August, when electricity
demands set records across the country. Daily maximum temperature
records were matched or broken every day for 11 consecutive days, from
Aug. 7-17, according to the National Climatic Data Center at the
National Oceanic Atmospheric Administration. Meanwhile, there were
droughts in the West, Southwest and Southeast.
On Aug. 16, water temperatures in the Tennessee River hit 90 degrees
Fahrenheit at Athens, Ala., forcing the partial shutdown of reactors
at the Browns Ferry Nuclear Plant. One reactor was shut down, and the
other two reactors had to reduce operations by 25 percent. Meanwhile,
Memphis and Nashville were experiencing record power demands.
Illinois, Michigan and Minnesota have scaled back nuclear plant
operations due to drought in the past two years, according to the
Union of Concerned Scientists, an advocacy group.
Nuclear plants in France, Germany, Sweden and Spain experienced
similar shutdowns because of water temperatures in 2006. And in 2003,
France shut down a quarter of its 58 nuclear power plants during a
heat wave, even after water-temperature regulations were softened to
"guarantee the provision of electricity of the country," according to
a government statement.
Power plants fueled by coal and natural gas also use plenty of cooling
water. Coal plants use about 750 gallons a megawatt hour and natural
gas more than 600 gallons a megawatt hour, according to the Electric
Power Research Institute (EPRI), an independent power and energy
research center supported by the electric industry.
Concerns about water demands have spurred opposition to power plants
proposed recently in Virginia, Idaho, the Great Lakes region and
Nevada.
Rising stakes
"We are using a resource that everybody needs," said Ed Legge, a
spokesman for the Edison Electric Institute, an association that
represents investor-owned utilities. "It is another one of the
important environmental issues we are going to need to address from a
supply standpoint and an environmental standpoint."
The U.S. thermoelectric industry withdraws 136 billion gallons of
freshwater per year, about 40 percent the country's total intake. But
power plants consume only about 3.3 billion gallons. By comparison,
agriculture accounts for another 40 percent of total freshwater
withdrawn and 84 percent of water consumption.
But every request to withdraw water is being more closely scrutinized
now.
There is more competition for that water, with the U.S. population
expected to increase by about 70 million over the next 25 years. And
with more people, there will be more demands for water for drinking,
recreation and resource protection.
At the same time, electricity suppliers are under pressure to build
more power plants. U.S. demand for electricity is expected to grow by
about 40 percent by 2030, the federal Energy Information
Administration says.
The industry is currently pushing to build baseload power plants
because of this increasing demand for electricity. Larger plants are
mostly expected to be coal or nuclear, Legge said, while new plant
construction in the 1990s was mainly smaller natural gas plants used
to supplement power during peak demand times.
The demand for new power plants is greatest in regions where water
supplies were strained by drought this summer -- the Southeast,
Southwest, and West, Legge said.
So why not rely on renewable energy sources? Legge said it is not
possible to provide the quantity or consistency of power that is
needed. And, moreover, some renewable power sources also rely on
taking in water.
While wind and solar photovoltaic technology use little or no water,
concentrated solar uses more than 700 gallons of water per megawatt
hour, according to EPRI. Concentrated solar technology uses reflective
surfaces to concentrate rays on a container full of a fluid.
Geothermal is also a significant water user. A University of
California, Santa Barbara, study of possible energy generation
portfolios that could meet California's goal of getting 33 percent of
its energy from renewable sources by 2020 found that geothermal, along
with coal, accounted for less than 25 percent of generation but over
90 percent of water intake.
Next wave?
Industry and government are searching for technological fixes to
water-energy crunch, according to interviews with engineers, and DOE
and industry literature. NETL's Feeley and researchers at 10 other DOE
laboratories have been analyzing the energy-water nexus for the past
four years.
About 30 percent of current U.S. generating stations use a
traditional, wet "open-loop cooling" system, according to DOE. The
system draws water from an adjacent water body, runs it through the
plant to condense the steam needed to power turbines and then returns
what is left to the water source. But the large water intake and the
high-temperature of the discharged water create problems for aquatic
life.
Most plants built since the 1980s have been using "closed-loop
cooling," which regulates temperature through evaporation in a cooling
tower. Such plants withdraw 5 percent of the water used by open-loop
systems, but most of what it withdraws evaporates. There is
considerable research to find ways to recapture the water lost to
evaporation in closed loop.
Researchers are testing a "dry cooling system" that uses air to cool
power plants. But the system is expensive to install and is 2 percent
less energy efficient, on average, than wet-cooling systems. A dry
cooling chamber is capable of chilling steam only to match surrounding
air temperature and becomes less efficient as outside temperature
rises. In very hot weather, dry-cooling plants may lose as much as 25
percent efficiency, DOE said.
There is also a hybrid system that uses dry cooling most of the time,
then switches to a wet system when the temperatures climb. Such
systems are expensive and may be difficult to permit, experts say.
Other alternatives include having plants cool themselves with
"nontraditional" water drawn from oil and gas production, coal mines,
municipal wastewater or other so-called gray water. Some Pennsylvania
power plants are starting to use mine water, Feeley said.
"At this point, it is difficult to pick winners," in water technology,
Feeley said. "You can look at the water-energy issue on the national
basis, but you also need to break it down on the regional basis,"
depending on temperature and water resources in each area.
But he added, "Through research and development we can reduce that
capital cost, make materials cheaper and achieve a higher degree of
heat transfer. There are improvements that can be made."
Copyright 1996-2007 E&E Publishing, LLC